Furnace



Patented Oct. 6, 1942 s PATENT OFFICE FURNACE Harold 4Griffin Elder,Chicago, and John Fred Mowat, La Grange, lll.,

i Application october z9,194o,seria1Ne.s63,337

(ci. 26a- 44) 3 Claims.

This invention relates to metallurgical furnaces and particularly to animproved metallurgical furnace of the bottom fired type sometimes calleda soaking pit for heating ingots and the like.

In some types of bottom fired furnaces or soaking pits, the fuel,usually gas or oil, is supplied thereto in a vertical stream through aport or burner located in the bottom of the heating chamber .centrallythereof. Surrounding .the stream of fuel in the pit or heating chamberthere is provided an annular column of preheated air which providesoxygen for delayed combustion, forming a long flame which risesvertically to the top wall or usually a removable cover for ychargingthe ingots or articles to be heated into the furnace whereby it isdeflected in an outward and downward direction by the cover in a mannerwell known to those skilled in the art with the flow being similar tothat of a fountain. The flame and products of combustion in the downwardpath pass between and around -the ingots Y against the inner side of thetop wall or cover, n and that the brickwork of the cover is subjected toextremely-high temperatures, particularly the central portion thereofimmediately above the firing port. For this reason the top wall or coverhas a relatively short life thereby resulting in high replacement andmaintenance costs, which is both undesirable and unsatisfactory, and isalso troublesome and inconvenient. Also, since the central portion ofthe cover cannot be cony veniently insulated lwithout increasing thedeterioration of the brickavork to a marked degree, there is anexcessive heat loss for the reason that the maximum flame temperatureoccurs at this' point, that is, where the flame first contacts thecover. Itis to a furnace or soaking pit 'having means incorporatedtherewith for protecting the inner side of the `top wall or cover fromthe direct impingement of this high temperature'ilame that the presentinvention relates.

Accordingly, it is one of vthe objects of the present invention toprovide an improved metallurgical furnace or soaking'pit having meansincorporated therewith for protecting the top wall or cover from theintense heat to which it is subliect, thereby reducing maintenance cost'thereof 55 to a minimum and, at the same ing excessive heat losses.

It is another object of the invention to provide an improvedmetallurgical furnace or soaking pit which is simple and inexpensive inits construction and use, and, at the same time, one that is mostefficient and effective.

It is a further object of this invention to provide an improvedmetallurgical furnace or soaking pit in which the circulation of the hotgases therein is increased, thereby resulting in a more thorough mixingof the gases and permitting gas dilution to any extent desired.

Variousother objects and advantages of this invention will become moreapparent in the course of the following specification and will beparticularly pointed out in the appended claims.

In the accompanying drawing, there is shown for the purpose ofillustration -and description one embodiment which our invention mayassume in practice.

In the drawing:

time, eliminat- Figure 1 is a vertical section through a metal-llurgical furnace or soaking pit with which the improved cover protectingmeans of our invention is shown incorporated;

Figure 2 is a horizontal section taken on the line II- II of Figure 1;and,

f Figure 3 is a horizontal section similar to Figure 2 showing a slightmodification in accordance with our invention.

Referring more particularly to the drawing, our

invention is shown incorporated with a conventionaltype furnace orsoaking pit for heating ingots and the like. Such a furnace or soakingpit comprises a heating chamber 2 usually rec- -tangular or square inshape which is adapted to b e center red at the 'bottom thereof by anysuitable means. In the present instance there is provided a pipe 3through which the fuel is supplied and directed z. into the heatingchamber through a relatively large port 4 where combustion of the fuelinitially takes place. The preheated air for combustion is directed andsupplied preferably from the recuperators 5 positioned to either side ofthe furnace through a horizontally disposed duct 6 arranged below thehearth and upwardly through the pori-,.4 around the outer side 0f thefuel pipe 3 into the heating chamber. There is provided preferably inthe opposed side walls of the furnace at the bottom of the heatingchamber outlet ports 1 which pref erably communicate with therecuperators 5J 'I'hus it will be seen that the flame fromthe burner orfuel supply pipe 3 is directed vertically upwardly to contact the innerside of the top Wall or removable cover 8 before the resulting productsof combustion descend and enter the recuperators through the outletports 1.

According to the present invention, there is arranged in two of theopposed side walls of the furnace adjacent the top thereof above therecuperators 5 and outlets ports 1, a supply pipe 9 having thevinner endthereof extending through an upwardly inclined port IIJ arranged in eachof the opposed side walls of the furnace with the outer ends of each ofthe pipes 9 connected to a suction fan I2 suitably mounted above therecuperators. There is arrangedin each of the supply pipes 9, preferablya valve I3 which is adapted to control the quantity and the velocity ofthe products of combustion passing therethrough from the suction fansI2. Each of the suction fans I2 is preferably connected to theirrespective recuperators 5 at the bottom thereof by means of a duct orpipe I4. Thus it will be seen that the suction fans I2 draw a relativelycool stream of products of combustion from the recuperators 5 and forceit through the pipes 9 into the heating chamber 2. It will be understoodthat the ports I0 together with the inner ends of the pipes 9 arrangedtherethrough, are vupwardly inclined and are constructed and arranged sothat the cooled streams of products of combustion supplied thereby willbe directed toward each other and upwardly toward the center of the topwall or removable cover 8 above the upwardly impinging iiame directedfrom the fuel supply pipe 3 so as to provide a protective screen betweenthis hot upwardly impinging ame and the inner side of the top wall orcover, thereby protecting the same from the intense heat of thisiiame.`-

In Figure 3 there is shown a slight modication of our invention. Thisconstruction is generally the same as that shown in Figures 1 and 2 butdiffers therefrom in that the ports I0 together with the inner ends ofthe air supply pipes 9 are angularly disposed relative to the side wallsof the furnace as shown so-as to produce a combined turbulent andwhirling effect of the hot gases within the heating chamber as'well asto provide a protective screen.

While the cooled products of combustion introduced into the furnace inthe manner'described are relatively cool as compared with'the-iiametemperature of the burning fuel, which may be rich gas, such as cokeoven gas, natural gas or refinery gas, or lean gas, such as blastfurnace gas or producer gas, or a mixture of Various combustible gases,or oil, they still will be ata temperature of from l000 to 1500J F.,which is high enough not to cause any undesirable cooling acshown anddescribed as the means for moving products of combustion, air or inertgases, it will temperature, an arrangement may be providedwhereby air,either at atmospheric temperature or preheated in recuperators, or otherheat exchange media, maybe introduced in thesame manner to promotesecondary combustion and to increase turbulence, or to acceleratecombustion, through automatic or manual proportioning 'of the totalamount of air introduced into the furnace. An arrangement may also beutilized whereby any combination of heated air and waste gas may beintroduced, with automatic or manual proportioning of the heated air andWaste gas so introduced and automatic or manual proportioning of the airin the mixture to the air introduced through the burner port, withregulation being accomplished through known means. In the same manner wemay proportion and mix the secondary air and waste gas or other gases tocontrol the temperature and the atmosphere may be proportioned asdescribed. Likewise it may be desirable to introduce inert gas, such asnitrogen, carbon dioxide or the like, to minimize oxidation of thematerial being heated.

At times pit furnaces or other heating furnaces of the bottom red typeare constructed without-any provision for waste heat recovery. In suchcases the fuel and cold air are introduced through a burner. When usedfor heating steel, such a burner is preferably of the long iiame type,Where slow mixing of the fuel and air delays combustion and through adeficiency of air in the mixture of fuel and air leaving the burnercauses cracking or reforming of the rich fuel used, with a resultantluminous ame. Such a iiame is much longer than the short sharpnonluminous iiame resulting from an intimate mixture tion in the heatingchamber, particularly since l the volume of products of combustionutilized is small compared to the total volume of products ofcombustion. Further, operating conditions are satisfactory, since themaximum temperature of about 1500 F. lies well within the safe operatingrange of mechanical equipment available for handling hot gases.

Although two fans and two streams of products of combustion are shown,it may, at times, be desirable to install additional fgis, or additionalducts from individual fans, either to take the cooled products ofcombustion from any number of recuperators, or other heat exchangemedia,lthat may be installed or to introduce the cooled products ofcombustion from various points in the furnace and, while fans have beenof fuel and air, which type of flame would have a very highly localizedtemperature zone adjacent the material being heated, with resultantwashing of the metal.

With the proper type of burner, the iiame must be longer and greater involume than when preheated air for combustion is used, if the same rateof heat input is to be maintained. This condition increases the dangerof thelong flame contacting the steel ingots or other material beingheated, with resultant probability of washing or burning the metal.Under such conditions, the introduction of secondary air by means of thepresent invention, as explained more indetail later, will acceleratecombustion, thus `minimizing the danger of damage to the steel.

As stated above, it may be desired to add waste gases from `the wasteheat fiue to the air to increase the volume and also the air temlence,with resultantfurther acceleration of combustion, and decreased dangerof damaging the material being heated.

Another advantage inherent in this invention lies in the increasedcirculation caused by the introduction of products of combustion bymeans of the fans, which circulation results in improved mixing of thegas and `air near the top of the heating chamber, with more rapidcombustion and a flame shortened in the latter stages, so that thedescending stream of gas consists only of products of combustion, thusavoiding the undesirable effect of having burning fuel contact thesteel. This advantage applies particularly to the recuperative type ofpit furnace when burning rich gas, in which case the ascending column ofgas is surrounded by an envelope of air, the combustion'occurringlargely as diffusion causes the air and gas to come in contact with eachother. This process is necessarily slow, as long as the two parallelstreams are not disturbed. In the present invention, it will be seenthat the ascending column of unmixed gas and air enters the zone wherethe high velocity streams of Waste gas meet, with the resultingturbulence causing an intimate mixture of the unburned gas and air, withaccelerated combustionbefore the gases reach the cover.

While we have shown and described one specii'lc embodiment of ourinvention, it will be understood that this embodiment is merely for thepurpose of illustration and description and that various other forms maybe devised within the scope of the invention, as defined in the appendedclaims.

We claim:

1. In a furnace of the class described for heating ingots and the likeincluding a heating chamber having side and top walls, a hearth arrangedcentrally of the heating chamber upon which the articles to be heatedare adapted to be placed, means arranged centrally ofsaid hearth forfir:- ing the furnace by a flame rising upwardly therefrom, and meansarranged in two of the opposed side walls of` said furnace adjacent thetop thereof substantially opposite eachother for supthorough combustionof the unburned fuel'gases before they contact the top wall of thefurnace.

2. In a furnace of the class described for heat',- ing ingots and thelike including a heating chamber having side and top walls, a heartharranged centrally of the heating chamber upon which the articles to beheated are adapted to be placed, means arranged centrally of said hearthfor ring the furnace by a flame rising upwardly therefrom, an upwardlyinclined port arranged in at least each of two of the opposed side wallsof said furnace adjacent the top thereof substantially opposite eachother, and means arranged with each of said ports for supplying arelatively cool stream of substantially inert gas or air therethroughand into the heating chamber toward the upper central portion thereofwhereby the stream of gas or air is directed upwardly toward the centerof the top-wall by the inclined ports so that the same will beinterposed between the flame and the top wall of said furnace and meetthe unburned gases of the flame at a point spaced from the top wallwhereby a turbulent action is provided so as to cause an intimatemixture of the inert gas and the unburned gases of the flame andthorough combustion of the unburned fuel gases before they contact thetop wall of the furnace.

3. In a furnace for heating ingots and the like, including a heatingchamber having side and top walls, a hearth arranged in said heatingchamber upon which the objects to be heated are adapted to be placed,means for directing fuel gases into said furnace chamber insubstantially a vertical plane for firing the'same, means for directingopposed streams of inert gas into said chamber adjacent the top thereofslightly tangential to each other and substantially perpendicular to thestream of -fuel gases being directed thereinto so that the streams ofinert gas and stream of' fuel gases will meet at a point spaced from thetop wall of the furnace whereby a whirling and turbulent action isprovided so as to cause an intimate mixture of the inert gases and theunburned fuel gases and accelerated combustion of the unburned fuelbefore they contact the top wall.

HAROLDAGRIFFm ELDER.

JOHN FRED MoWAT.

